Oxalobacter formigenes is a gram-negative, anaerobic bacterium inhabiting the gastrointestinal tracts of most, it not all, vertebrates, including man. This bacterium plays an important symbiotic relationship with its hosts by regulating the absorptive and secretory pathways for oxalic acid in the intestines, thereby maintaining homeostatic levels in plasma. The absence of this bacterium from the gut has been shown to correlate with hyperoxaluria and an increased frequency of first-time and recurrent calcium oxalate kidney stones; consequently, the absence of O. formigenes appears to be a risk factor for urolithiasis. Epidemiological studies of O. formigenes colonization in humans have pointed to several important observations: humans normally become colonized as young children; virtually all children can become colonized naturally; colonization rates in adult populations ranges only between 60-80% worldwide; and, colonization is especially sensitive to changes in the GI tract and the use of antibiotics. In 2003, clinical trials using O.formigenes in the treatment of hyperoxaluria in children with primary hyperoxaluria provided encouraging results, thus raising the specter that this bacterium may be effective in treating calcium oxalate kidney stone disease with enteric hyperoxaluria as an underlying cause. One such population is the subgroup of irritable bowel disease (IBD) patients that develop kidney stones. The studies being proposed in this exploratory R21 grant application are in response to NIDDK Program Announcement PA-03-065, one goal of which is to develop new animal models that may help clarify etiologic factors underlying oxalate stone disease in patients with bowel disease and the identification of improved prevention and therapy options. To this end, we are proposing to determine if (a) the IL-10 gene KO mouse, known to share many features with human Crohn's disease, represents an adequate animal model for the study of hyperoxaluria and calcium oxalate kidney stone disease associated with IBD, and (b) O. formigenes is an effective intervention treatment for reducing hyperoxaluria and/or calcium oxalate crystaluria under conditions that may exist in human patient populations with IBD. By defining the inter-relationships between O. formigenes and the host when the host has IBD, we will be able to define limitations and/or the possible risks of using this bacterium in "probiotic-like" therapies to treat hyperoxaluria in patients with IBD. [unreadable] [unreadable] [unreadable]